Hypotheses

The main hypotheses of the US GLOBEC NEP program focus on the relationships between physical and biological variations. While several recent publications demonstrate correlative links between these variations, the physical mechanisms and the key oceanic processes that instigate and sustain population fluctuations are not clear. Furthermore, there is still much to be learned about interactions between the environment and biota on interannual to interdecadal scales. Our hypotheses are listed below, separated into five main areas.

I. PATTERNS

a. Differences in the mean structure and circulation of the subtropical and subarctic gyres of the north Pacific lead to significant differences in the gyres' responses to decadal forcing.

b. Decadal variations in Ekman pumping, mixed layer depth, and other biologically key physical quantities tend to be out of phase in the subarctic and subtropical gyres.

c. There are significant large-scale decadal variations in the California and Alaska Currents.

II. MECHANISMS AND SOURCES

a. Remote, large-scale processes in the ocean and atmosphere control decadal variability in the NEP. Local processes are a secondary contributor to this variability.

b. Decadal fluctuations in the transport of the West Wind Drift contribute significantly to changes in the structure and circulation of the California Current System and the Alaska Gyre.

c. Basin-scale fluctuations have major impacts on the coastal mesoscale processes in the NEP that enhance biological productivity.

III. REGIONAL DIFFERENCES

a. The impacts of basin-scale processes on the NEP are not uniform, but have regional decadal manifestations determined by interactions between basin-scale signals and regional differences in atmospheric forcing, ocean structure, and circulation.

IV. SEASONAL DIFFERENCES

a. The amplitude and phase of seasonal cycles of key physical parameters in the NEP are altered by decadal variations.

V. DECADAL AND SHORTER-TERM VARIABILITY

a. The basic mechanisms of decadal variability in the NEP are similar to those that produce shorter term (e.g., one to three year) variability, although the initiation regions, processes, or impacts may be different.